1. Field of the Invention
The present invention relates to a zoom lens barrel and more particularly to a zoom lens which has a diaphragm mechanism provided on a lens unit to be shifted in zooming in an optical axis direction and to be shifted in focusing in the optical axis direction while being rotated, and has a mechanism for correcting an aperture diameter during zooming.
2. Related Background Art
Conventionally, in a zoom lens barrel adopting a focusing system called "whole element focusing" or "front element focusing", a diaphragm mechanism is held on a lens unit shifting frame not to be rotated in zooming and focusing.
In this type of diaphragm mechanism, its aperture diameter is varied by rotating a supporting member of aperture blades of the diaphragm mechanism by means of a lever with a cam surface from a fixed barrel containing the lens unit shifting frame, or another lens unit shifting frame not to be rotated.
On the other hand, recently, a zoom lens barrel adopting a focusing system called "internal focusing" has been proposed in which the zoom lens is made compact and a taking range is enlarged by varying the focal length of lens units and reducing the amount of shift of the lens units.
However, in the conventional internal focusing zoom lens barrel, a lens unit holding a diaphragm mechanism is not rotated in zooming but rotated in focusing. Therefore, the diaphragm mechanism is rotated in focusing. However, in this case, it is difficult to correct the aperture diameter by means of the conventional diaphragm mechanism and various problems have occurred.